Mr Shapps told the Prime Minister in his resignation letter that the "buck should stop with me" over issues while he was Conservative Party chairman.

It has been alleged that Mr Shapps mishandled claims that young activist Elliott Johnson - who died in September - was bullied. 

The allegations of bullying relate to claims Mr Johnson was bullied by Tory youth organiser Mark Clarke, who denies any wrongdoing.

Mr Shapps - former party chairman - resigned after Mr Johnson's father, Ray, called for him to go along with the current party chairman Lord Feldman.

He insisted his son would still be alive if they had acted properly.

In his letter to David Cameron, Mr Shapps wrote: "Although neither the party nor I can find any record of written allegations of bullying, sexual abuse or blackmail made to the chairman's office prior to the election, I cannot help but feel that the steady stream of those who raised smaller, more nuanced, objections should have perhaps set alarm bells ringing sooner.

"In the end, I signed that letter appointing Mark Clarke 'director of Road Trip' and I firmly believe that whatever the rights and wrongs of a serious case like this, responsibility should rest somewhere.

"Over the past few weeks - as individual allegations have come to light - I have come to the conclusion that the buck should stop with me."

Mr Clarke is accused of bullying Mr Johnson in the months before he is believed to have killed himself.

He was named in a letter written by the young activist just before he died on railway tracks on 15 September.

The Conservatives have always claimed they were not aware of any complaints against Mr Clarke before August, when Mr Johnson made an official complaint to Conservative Campaign Headquarters (CCHQ).

However, it emerged earlier this week that Conservative peer Baroness Warsi, a former party chairman, had written a letter in January complaining about Mr Clarke abusing her on Twitter.

In addition, Conservative aides were warning about Mr Clarke, who was dubbed "Tatler Tory" after the magazine named him as one to watch for the future, as far back as 2008 when he was an election candidate for Tooting.

He failed to gain the seat at the 2010 General Election.